1. Technical Field
The present invention relates to electro-optical devices and electronic apparatuses which display images.
2. Related Art
As an example of an electro-optical device including an electro-optical element whose optical property is changed by electric energy, a liquid crystal display device is known. A liquid crystal display device includes a plurality of data lines, a plurality of scanning lines, and pixel circuits provided at intersections of the data lines and the scanning lines. Each pixel circuit includes a selection transistor and a liquid crystal element, which is an electro-optical element. The selection transistor is controlled to be in an on state or an off state in accordance with a scanning signal supplied via the scanning line. When the selection transistor is in an on state, an image signal supplied via the data line is applied to the liquid crystal element; when the selection transistor is in an off state, a voltage of the image signal is held in the liquid crystal element. In other words, during a period from when the image signal is written into the pixel circuit to when the image signal is written thereinto next time, the voltage of the image signal which has been written is held in the liquid crystal element, whereby the liquid crystal element is controlled to have a transmittance corresponding to the voltage of the image signal. In an operation of an electro-optical device, a plurality of scanning lines are sequentially selected, and an image signal is written via a data line to a pixel circuit corresponding to the selected scanning line. Thus, the voltage of the data line changes every horizontal scanning period.
The data line is a capacitive load; therefore, a precharge voltage may be written into the data line before writing of the image signal. In other words, one horizontal scanning period may be divided into a precharge time in which the precharge voltage is supplied to the data line, and a write time in which the image signal is supplied to the data line.
Further, as a method for writing image signals into a plurality of data lines, a dot-sequential method and a phase-expansion method are known. In an electro-optical device employing a dot-sequential method, a plurality of switches are provided between one image signal line to which an image signal is supplied and a plurality of data lines; the switches are sequentially turned on exclusively, whereby the image signal is sampled and supplied to each data line. In an electro-optical device employing a phase-expansion method, a plurality of data lines are divided into blocks, and the image signal is supplied to the data lines per block. For example, in a phase-expansion method of six phases, one image signal is subjected to serial-parallel conversion into six phase image signals, and the image signals are supplied to six image signal lines. One block includes six data lines, and switches are provided between the data lines and the six image signal lines. Six switches in each block are turned on at the same time and the six phase image signals are written into the six data lines per block at the same time. In such a manner, in a dot-sequential method and a phase-expansion method, image signals are written a plurality of times during one horizontal scanning period.
The data line and the liquid crystal element are capacitively coupled via a parasitic capacitance. Therefore, if the voltages of data lines change in a period from when image signals are written into pixel circuits of a scanning line to when image signals are written thereinto next time, the voltages of the image signals held in the liquid crystal elements vary due to capacitive coupling. As a result, the display image quality is decreased. Specifically, in a liquid crystal display device, a polarity inversion driving method is employed where a polarity of the image signal is inverted about a reference level at a predetermined interval (e.g., at each field). In such a case, the voltages of the data lines greatly vary, which may cause so-called vertical cross-talk.
In order to reduce vertical cross-talk, a technique is known where image data for one field is stored in a large-capacity memory, and vertical cross-talk is corrected using the image data for one field stored in the memory (see, for example, JP-A-2000-330093 and Japanese Patent No. 3869464).
In addition, a technique is also known where, in a liquid crystal display device which displays the same image in a first field and a second field, two small-capacity memories are used, and vertical cross-talk is not corrected in the first field and is corrected only in the second field (see, for example, Japanese Patent No. 4816031).
However, in a dot-sequential method and a phase-expansion method, if a precharge voltage is written before writing of an image signal, a length of a period from writing of the precharge voltage to writing of the image signal differs with a position of the data line in a horizontal direction. In addition, since a leakage current flows through a switch between the image signal line and the data line when the switch is off, the voltage of the data line changes as time passes from writing of the precharge voltage to writing of the image signal. As a result, there has been a problem in that vertical cross-talk cannot be reduced sufficiently.